Approximately five million children are born each year in the United States alone. Historically, childbirth carried a significant risk of complications, but this risk has substantially abated with the advancement of modern science and technology. For example, monitoring equipment employed during the childbirth process has been instrumental in reducing the risk of childbirth complications. Information used to assess labor includes contractions of muscles such as the maternal uterus and the fetal heart. Such muscular contractions may create an electromagnetic field that can be detected, although typically the electromagnetic fields created by the maternal uterus and fetal heart are relatively weak and are difficult to detect directly.
One type of monitor is a contraction monitor, which monitors the contractions of the uterus throughout the labor process. The contraction monitor provides real-time information regarding the strength and spacing of contractions, which may permit evaluating the progression of the labor and identifying potential complications. Another example is a fetal heart rate monitor, which provides real-time information regarding the rate of the fetal heart beat so that fetal distress may be identified.
One problem with conventional monitoring equipment is that it may not be suited for use with obese patients or other patients having large deposits of fat in the abdominal area. For example, a tocodynomometer is a contraction monitor that detects contractions by measuring changes in the curvature of the abdominal wall. Although highly effective for most patients, the tocodynomometer may not be effective for obese patients, as layers of fat about the abdomen may impede the detection of abdominal wall curvature changes. Another contraction monitor employs electromyographic (EMG) sensors placed on the surface of the patient's abdomen, which measure changes in electrical surface potential caused by uterine contractions. The effectiveness of EMG sensors may be substantially reduced in obese patients, as abdominal fat may increase the distance between the EMG sensors and the uterus, obscuring detection of the contraction signal. Fat also may have a relatively high impedance, distorting the electrical signal associated with the contraction or decreasing its amplitude. These monitors may be especially ineffective at detecting relatively weak contractions in obese patients, such as early labor contractions, Braxton-Hicks contractions, or false labor contractions. Thus, it may be difficult to identify whether an obese patient has truly begun the labor process.
Regarding the monitoring of fetal heart rate, one common monitor employs an EKG electrode attached directly to the head of the fetus within the uterus. Because the electrode is attached internally, the monitor is not suited for use until the membranes of the laboring patient have ruptured. Thus, fetal heart rate may not be monitored until the labor has advanced past the initial stages. For earlier stages of labor, external fetal heart rate monitors have been developed that use technology such as ultrasound. Ultrasound monitors provide a linear beam of ultrasound that is directed at the fetal heart. The maternal abdominal wall may not have a uniform curvilinear surface in an obese patient. If the fetal heart is located near the panniculus of abdominal fat deposits, the ultrasound device may shift position during labor. These position shifts are common in obese patients and may result in periodic inability to detect even the presence of a fetal heart rate during labor. When used on obese patients, both contraction and fetal heart rate monitors suffer from the drawbacks described above. Thus, a need exists for systems and methods of detecting labor conditions as disclosed and claimed below.